1. Field of the Invention
The present invention relates to an adsorptive fiber sheet wherein a nonwoven fabric of synthetic fiber constituted only by synthetic fiber having a higher melting temperature is secured in a layered structure to at least one surface of a nonwoven fabric of adsorptive fiber which is produced in such a manner that synthetic fiber having a higher melting temperature, synthetic fiber having a lower melting temperature and adsorptive fiber are mixed with one another and contact points between the synthetic fiber having a lower melting temperature and other fibers are bound together by softening the synthetic fiber having a lower melting temperature.
2. Description of the Prior Art
Heretofore, pulverized or granular activated carbon and ion exchange resins are widely known in the art as adsorbent for removing various kinds of foreign materials such as bad-smelling components, coloring components and specific noxious chemicals in gas or liquid. In order to use these activated carbon and ion exchange resins as means for removing bad-smelling components, coloring components and specific noxious chemicals in gas or liquid, they are charged in a defined section between filter-shaped members disposed in a passage for gas flow or liquid flow which is generated by a pump. However, since they are adapted to function as adsorbent in the defined section, there is a need of providing a considerably high intensity of pressure for feeding gas or liquid or there is another need of allowing the adsorbent to be prepared in a comparatively large granular size, resulting in an adsorbing efficiency being reduced. It should be noted that these drawbacks are unavoidable.
To obviate the drawbacks as mentioned above, a technique as disclosed in the official gazette of Japanese Utility Model Publication No. 2025/1982 which was published in 1982, has been developed. This latest technique is concerned with an adsorptive filter sheet which is so constructed that a felt-shaped protective and dust collecting filter comprising glass fiber is placed on one surface or both surfaces of a felt-shaped sheet comprising activated carbon fiber to build a layered structure and the former is lightly attached to the latter by needle punching. However, it is found as an inconvenience that the obtained adsorptive filter sheet can not be used for a long period of time because the activated carbon fiber is not adhesively secured to other fibers and easy to be damaged or injured.